2015-03-31T20:49:35ZCharacterization of flow-induced vibrations in gas-solid fluidized beds: elements of the theoryhttp://hdl.handle.net/10016/20239
Characterization of flow-induced vibrations in gas-solid fluidized beds: elements of the theory
Villa Briongos, Javier; Sobrino, Celia; Gómez Hernández, Jesús; Santana Santana, Domingo Jose
This paper revisits the basic hypothesis underlying the measurement of flow-induced vibration in fluidized beds. A novel theoretical approach based on the standing pressure field characterizing the bed dynamics is proposed to link the pressure fluctuations to the measured accelerometer signals. The model provides a reliable prediction of the carrying frequency band and helps in designing the accelerometer measurement process. The model was tested with previous results reported in the literature as well as with piezoelectric accelerometer measurements collected from a lab-scale experimental facility. A study on accelerometer measurements was conducted to identify the main limitations expected for measuring flow-induced vibrations in a gas-solid fluidized bed. The structural response of the vessel to flow-induced vibration was mostly determined by the "bed acoustics" that can be dominated by either elastic or compression waves. Finally, the survival of an envelope process on the measured accelerometer signal guaranteed the quality of the flow dynamical information collected during the measurement process.
2013-01-01T00:00:00ZThermal energy storage in a fluidized bed of PCMhttp://hdl.handle.net/10016/20238
Thermal energy storage in a fluidized bed of PCM
Izquierdo-Barrientos, María Asunción; Sobrino, Celia; Almendros-Ibáñez, José Antonio
The objective of the present work was to research the storage behavior of a fluidized bed filled with a granular phase change material (PCM) with a small particle diameter (d(p) = 0.54 mm). The performance of the fluidized bed was compared to that of well-known storage methods such as fluidized beds with sand and packed beds based of sand and PCM. For this purpose, heating experiments were conducted in a cylindrical bed with air as the working fluid. The influence of the bed height and flow rate on the storage and recovery efficiencies of the fluidized bed of PCM was analyzed. Additionally, the stability of the PCM during various charging-discharging cycles was studied. The results indicate that this PCM is an alternative material that can be used in fluidized bed systems to increase the efficiency of storing thermal energy in the form of latent heat. Under the experimental conditions tested in this study, higher charging efficiencies were observed for fixed and fluidized beds based on PCM than those of sand. High gas velocity and low bed height shorten the charging time but also reduce the charging efficiency. The cycling test shows that the PCM is stable under bubbling conditions up to 15 cycles, which corresponds to approximately 75 h of continuous operation.
2013-08-01T00:00:00ZDefluidization and agglomeration of a fluidized bed reactor during Cynara cardunculus L. gasification using sepiolite as a bed materialhttp://hdl.handle.net/10016/20154
Defluidization and agglomeration of a fluidized bed reactor during Cynara cardunculus L. gasification using sepiolite as a bed material
Serrano, Daniel; Sánchez-Delgado, Sergio; Sobrino, Celia; Marugán-Cruz, C.
This work studies the defluidization time and the agglomerate generation in a bubbling fluidized bed (BFB) reactor during Cynara cardunculus L. gasification using, separately, two different bed materials, silica sand and sepiolite 〖(MG〗_8 〖Si〗_12 O_30 (OH)_4 〖(OH〗_2)(_4^)8 H_2). The high adsorption capacity and the elemental composition of the sepiolite make it suitable as an alternative bed material in order to reduce agglomeration. Experiments were performed on a stainless steel lab-scale BFB reactor operating with air as a gasifying agent at different air excess ratios (u/umf). A quartz reactor was alternatively used for the visualization of bed material and biomass during gasification, allowing one to observe the agglomerate formation process. Pressure signals were analyzed both in time and frequency domain to determine the defluidization time. Furthermore, the shape and size of the bed material after the experiments were evaluated. Higher defluidization times in the case of sepiolite were measured. Particle sizes were affected by the type of bed material and the air excess and agglomerates of different shapes were formed for sepiolite and silica sand.
2015-03-01T00:00:00ZExperimental heat transfer coefficients between a surface and fixed and fluidized beds with PCMhttp://hdl.handle.net/10016/20153
Experimental heat transfer coefficients between a surface and fixed and fluidized beds with PCM
Izquierdo-Barrientos, María Asunción; Sobrino, Celia; Almendros-Ibáñez, José Antonio
This work presents an experimental study to determine the capacity of a phase change material (PCM) in granular form to be used in fixed and bubbling fluidized beds for thermal energy storage. The experimental measurements are focused on determination of the heat transfer coefficient between a heated surface immersed in the bed and the granular PCM. The flow rate is varied to quantify its influence on the heat transfer coefficient. The PCM used is Rubitherm GR50 with a phase change temperature of approximately 50° C. The PCM is available in two different particle sizes, 0.54 mm and 1.64 mm, of which the finer is used in the fluidized bed and the coarser is used in the fixed bed. In addition, the results obtained for the PCM are compared with the heat transfer coefficients measured for sand, a material commonly used for thermal storage. In comparing the heat transfer coefficients for fixed and fluidized beds, the heat transfer coefficients in the fluidized bed with PCM are nearly three times higher than those for the fixed bed at the same gas flow rate. This increase in the heat transfer is a result of two main factors: first, the continuous renewal of PCM particles from the heated surface when they are fluidized, and second, the large quantities of energy in latent form absorbed by the PCM. In the fixed bed there is no renovation of particles, consequently only a small percentage of particles are able to change its phase. Hence, there is no increase in the heat transfer coefficient due to this fact.
2015-03-01T00:00:00Z